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CELL MEMBRANES and TRANSPORT

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Title: CELL MEMBRANES and TRANSPORT


1
CELL MEMBRANESandTRANSPORT
2
The Cell
3
Cell Membrane
  • All living things are surrounded by a membrane.
  • A cell membrane is also known as plasma
    membrane.
  • Controls exchange of materials such as nutrients
    and waste between cells and their environment.
  • Has other important functions
  • for example to enable cells to receive hormones.

4
Cell Membrane
  • Fluid Mosaic Model - proteins embedded in a
    phospholipid bilayer.

5
Fluid mosaic model
  • FLUID- because individual phospholipids and
    proteins can move around freely within the layer,
    like its a liquid.
  • MOSAIC- because of the pattern produced by the
    scattered protein molecules when the membrane is
    viewed from above.

6

Cell membranes are made of PHOSPHOLIPIDS
  • HYDROPHILIC heads (water liking)-Attracted to
    the water
  • HYDROPHOBIC tails (water fearing)-repel water

A Phospholipid
7
A Phospholipid Bilayer
  • Phospholipids can form
  • BILAYERS
  • -2 layers of phospholipids with hydrophobic tails
    protected inside by the hydrophilic heads.
  • The PHOSPHOLIPID
  • BILAYER is the basic
  • structure of membranes.

8
  • Bilayer 2 layers of phospholipids
  • The heads stay on the outside and the tails stay
    on the inside.

9
Cell Membrane
  • Cell surface proteins
  • a. Channel proteins - transport food and other
    molecules into the cell and transport wastes out
    of the cells.
  • b. Receptor proteins - gather information about
    the cells surroundings.
  • c. Cell surface markers - identify the type of
    cell, important for cell recognition.

10
Movement of selected molecules across the cell
membrane
11
Cell Membrane
  • Permeability of the cell membrane
  • 1. Semi permeable/selectively permeable - only
    certain substances can pass across the membrane.
  • 2. Factors that determine whether a molecule can
    pass through a membrane or not
  • a. size
  • b. type

12
Transport Mechanisms
  • Transport Mechanisms - moving material in and out
    of the cell
  • Concentration gradient - the difference in the
    amount of a substance inside and outside of the
    cell
  • 1. Going with the gradient-moving from high to
    low concentration
  • 2. Going against the gradient-moving from low
    to high concentration
  • 3. Equilibrium exists when the concentration of
    molecules is the same throughout a space (inside
    and outside the cell)

13
Transport Mechanisms
  • Two categories of transport based on
    concentration gradient and the need for energy
  • 1. Passive transport does not require energy
  • goes with the gradient.
  • 2. Active transport requires energy
  • goes against the gradient.

14
Methods of Transport Across Membranes
  • 1. Diffusion
  • 2. Osmosis
  • 3. Facilitated Diffusion
  • 4. Active Transport

15
Methods of Transport Across Membranes
  • Diffusion -passive transport - no
  • energy expended
  • 2. Osmosis - Passive transport of water
    across membrane
  • Facilitated Diffusion - Use of proteins to
  • carry molecules or ions across
  • Active Transport- requires energy to
  • transport molecules against a
  • concentration gradient energy is
  • in the form of ATP

16
Types of Transport
17
Passive Transport Mechanisms Diffusion
  • Movement of molecules from an area of high
    concentration to an area of low concentration.
  • Movement from one side of a membrane to another
  • Example smoke across a room, food coloring
    dropped into water, oxygen in lungs

18
Diffusion
Diffusion in action
19
Passive Transport MechanismsOsmosis
  • Diffusion of water
  • Direction of osmosis-the direction of water flow
    depends upon the concentration of solute and
    solvent (water)
  • Tonicity-term used to compare 2 solutions
    (usually the inside and the outside of the cell)
  • a. Hypotonic - less solute (more water)
  • b. Hypertonic - more solute (less water)
  • c. Isotonic - equal amounts of solute and water

20
Passive Transport MechanismsOsmosis
  • Water will flow from a hypotonic solution to a
    hypertonic solution
  • Will water move in an isotonic solution?
  • Yes, but it wont be noticeable-equilibrium is
    established

21
Osmosis
How Osmosis works
22
Solutions
  • Solutions are made of solute and a solvent
  • Solvent - the liquid into which the solute is
    poured and dissolved.
  • Solute - substance that is dissolved or put into
    the solvent.
  • Salt and sucrose are solutes.

23
Passive Transport Mechanisms
  • Turgor pressure/osmotic pressure-pressure due to
    water in cell.
  • Analogy air pressure in a tire.
  • When a cell has high turgor pressure, it is
    bigger and stiffer.
  • When a cell has low turgor pressure, it is
    smaller and flimsy.

24
Passive Transport Mechanisms
  • Plasmolysis - wilting of a cell due to loss of
    turgor pressure
  • Cytolysis - bursting of a cell due to an increase
    in turgor pressure.
  • How do plant cells avoid cytolysis? Cell walls
  • How do unicellular freshwater organisms avoid
    bursting? Contractile vacuoles.

25
Plant and Animal Cells put into various
solutions
26
Passive Transport Mechanisms
27
Passive Transport Mechanisms
28
Passive Transport Mechanisms
  • Facilitated diffusion - transport of specific
    molecules across a membrane with the help of a
    channel protein
  • An example of a molecule that is often
    transported in this manner is glucose

How Facilitated Diffusion Works
29
Active Transport Mechanism
  • Active Transport Mechanism(requires energy in
    the form of ATP)
  • Ex.
  • Sodium-potassium pump - pumps sodium ions out and
    forces potassium ions in.
  • Important for conducting nerve impulses and
    muscle contraction.
  • Proton pump-transport protons through membranes
    of chloroplasts and mitochondria

30
Active Transport Mechanism
  • Endocytosis - process of bringing larger
    molecules into the cell by engulfing them.
  • 1. Pinocytosis liquids
  • 2. Phagocytosis - solids
  • amoebas eat this way
  • white blood cell engulf bacteria
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